Doppler-free two-photon absorption spectroscopy of trans-glyoxal under magnetic fields up to 6T

Abstract

In order to measure the Doppler-free two-photon absorption (DFTPA) spectrum in the presence of a strong magnetic field, a sample cell placed in an optical resonator was installed at the centre of the bore of a superconducting magnet capable of generating a magnetic field of up to 6T. Changes in spectra of the A 1Au ← X 1Ag transition of trans-glyoxal were measured as a function of magnetic field strength. Level crossings induced by Zeeman energy shifts were observed. The perturbing level, which shows hyperfine splitting, was identified as the 3Au(nπ*) state, because the hyperfine splitting is small in the 3Bu(ππ*) state and large in the 3Au(nπ*) state. The perturbation between the A 1Au(nπ*) and 3Au(nπ*) states was shown to take place by either vibronic interaction or Zeeman interaction between the 3Au(nπ*) state and the 3Bu(ππ*) component mixed to the A 1Au(nπ*) state by spin-orbit interaction. The magnetic moment of the A 1Au state was determined to be approximately 0.0028μB, and the magnitude of the mixing coefficients ⟨1 3Bu|H so|1 1Au⟩/[E(1 1Au) − E(1 3Bu)] was evaluated to be 0.026.